1. Field of theInvention
The present invention relates to a process for producing p-acetylaminophenol, and more particularly, to a process for producing p-acetylaminophenol by isomerizing p-aminophenyl acetate.
2. Description of the Related Art
There are known various processes for producing p-acetylaminophenol.
Representative processes are:
(1) A process of reacting p-aminophenol with acetic anhydride (for example, U.S. Pat. No. 3113,150, etc.);
(2) A process of dehydration-condensation of p-aminophenol and acetic acid;
(3) A process for reducing p-nitrophenol in the presence of acetic anhydride simultaneously with acetylation [Morris Freifelder: J.Org. Chem., Vol. 27, p. 1092 (1962), U.S. Pat. No. 3,076,030, etc.]; and
(4) A process for producing p-acetylaminophenol by rearrangement (Beckmann rearrangement) of an oxime compound in the presence of an acid catalyst, the oxime compound being prepared from p-hydroxyacetonone and hydroxylamine (Eur. Pat. Appl. EP 168,908, etc.).
Among the above-mentioned processes, process (1) is one of the processes widely used in the industrial production. There also are various processes other than above.
A process starting from p-aminophenyl acetate would appear to be suitable as an industrial production process from the standpoints of the starting material and the process step. However, little was known about processes for isomerizing p-aminophenyl acetate to form p-acetylaminophenol. Only one report is described in J. Org. Chem., 26, 1656 (1961) which discloses that it was contemplated to obtain p-aminophenyl acetate by the catalytic reduction of p-nitrophenyl acetate in the presence of platinum oxide as a catalyst in absolute ethanol at a pressure of 60 kg/cm.sup.2 of hydrogen at 120.degree. C. However, p-aminophenyl acetate was not obtained and instead p-acetylaminophenol was produced in a 77 % yield. This fact suggests that p-aminophenyl acetate was in situ isomerized to p-acetylaminophenol.
However, according to our investigation as shown below, it has been found that the isomerization is not effective. That is, when p-aminophenyl acetate prepared separately was isomerized simply by heating p-aminophenyl acetate in an organic solvent, p-acetylaminophenol was formed but at a remarkably slow speed and not in high yield.
For example, FIG. 1 shows a speed of production of p-acetylaminophenol when 0.05 mol. of p-aminophenyl acetate was heated in 15 g. of ethyl cellosolv at 120.degree. C. As is clear from this result, even after 6 hours of the reaction, the production percentage of p-acetylaminophenol is as low as about 40%.
The production percentage, i.e. "production (%)", in the ordinate of FIG. 1-FIG. 4 indicates how much percent of the starting material, p-aminophenyl acetate, is isomerized to p-acetylaminophenol.
Further, in other solvents the results were also almost the same as above, which indicates that the formation of p-acetylaminophenol by catalytic reduction of p-nitrophenyl acetate disclosed in the above-mentioned literature reference involves some other mechanism as well as the isomerization of p-aminophenyl acetate.